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Near Surface Geoscience 2016 - 22nd European Meeting of Environmental and Engineering Geophysics
- Conference date: September 4-8, 2016
- Location: Barcelona, Spain
- Published: 04 September 2016
61 - 80 of 189 results
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Numerical-experimental Study of Seismic Surface Waves Observables on Horizontal-vertical Components for Cavity Detection
Authors C. Filippi, D. Leparoux, G. Grandjean, A. Bitri, D. Pageot and P. CôteThe detection of underground cavities is still a challenging problem despite the good potential of geophysical techniques. The seismic surface waves analysis method can be acceptable for the cavity localisation if observables in data are affected by the void. We propose here a combined approach based on numerical 3D simulations (Spectral Finite Element Method) and reduced-scale experimental data to assess the possible observables affected by the cavity presence. The measurement bench MUSC is designed to effectuate seismic data measurements on reduced scale models on the two component of a P-SV configuration. We highlight different observables all visible in numerical or experimental cases: 1) the diffraction event is higher on the horizontal component; 2) there is a perturbation of the direct wavefield amplitude above the cavity and after the cavity position; 3) the analyse of the elliptic particular movement is perturbed in terms of amplitude and direction above and few meters after the cavity. Test results demonstrate the capability of using different observables of the Rayleigh wavefield in presence of a cavity to detect the object. These qualitative characteristics confirm the interest to study and compare observables on the horizontal and vertical components in a medium containing a cavity.
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Application for Capacitively Coupled Resistivity Surveys in the City of Messina
Authors D. De Domenico, G. Garilli, A. Teramo and A. MarinoThe electrical surveys by means of the OhmMapper Geometrics were carried out in the urban centre of the Messina city. The obtained results show an increased level of vulnerability of sediment areas due to the reduced depth of the water table in zones close to the coastline, also according to the hydrogeological characteristics of the urban area, which is crossed by nine seasonal streams. An additional safety reducer was highlighted by the presence of large area of the city where the buildings, also strategic buildings, have foundation partially or totally immersed in ground water table or water leakage from the municipal water. The CCR measurement can therefore be a useful supplement during the delineation of groundwater protection areas in urban sites where the telluric noise and the very dry shallow layer make the more traditional galvanic method impracticable. The main advantage of CCR is a more simple experimental setup, which allow a deeper insight into underground structure and results in a more time and cost effective geoelectrical logging.
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Evaluation of KTU Farabi Hospital Building Strength Comparing of the Ground by Using Single Station Microtremor Method
More LessDetermination of ground and building characteristics is important to provide against earthquakes. KTU Farabi Hospital is located in Trabzon and approximately 150 km distance from the North Anatolian Fault which is the most dangerous fault system in Turkey. In this study, 10 microtremor recordings were collected in the building and ground. The measurements taken in the building were recorded at (-2)nd, 1st, 4th, 7th, 11th floors and repeated day and night except 1st and 7th floors. The recordings were evaluated with Geopsy program according to Nakamura Method. The predominant frequencies were obtained averagely 1.66 Hz for the building and 7.65 Hz for the ground. The resonance risk is low because these two average frequencies are not close to each other. The damping ratios were calculated by using Half Power Method. The damping ratios are matching with the predominant frequencies and averagely 0.09% for the building and 0.23% for the outside points. Finally, the horizontal components of the all measurements were divided by each other to detect transfer function of the building to Floor Spectral Ratio Method. According to this dividing it can be said that the predominant frequencies are almost the same with the predominant frequencies obtained from Nakamura Method.
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Odd-even Pole-pole Array and 3D Resistivity Surveys in Urban and Historical Areas
Authors F. Almeida, N. Barraca, R. Moura and M.J. Senos MatiasModern and historical buildings may show some degree of subsidence resulting from foundation deterioration and local geological conditions. Hence, buildings stability can be affected and restoration plans must be envisaged. Resistivity methods have been used to investigate local conditions, providing 3D images of the soil under man made structures and hence contributing to the delimitation of hazardous areas and pathologies. However these techniques require the deployment of a grid of electrodes, which can be difficult to accomplish because of physical limitations and of the buildings nature that cannot be damaged. To overcome these problems special arrays have been used (L, Corner, Square arrays, etc). Here in it is proposed to use the “Odd-Even Pole-Pole Array” to study the ground under a contemporary building and under a high historical value XIV century Abbey, both showing evidence of subsidence. Field data quality is also addressed and it is proposed to identify low quality data to be expunged so that modelling is improved. It is also shown how to estimate resistivity values from data quality tests, to carry out further zonation, locate hazardous areas and to enhance modelling.
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Megalopolis Influence on Geophysical Field Variations
Authors S.A. Riabova, D.N. Loktev and A.A. SpivakThe research of geophysical fields in the conditions of megalopolis attracts particular interest not only in terms of their influence on the operation of precision equipment and technological processes associated with nanotechnology, but also it is perhaps the most important in terms of the formation of special habitat of human and other biological objects. Indeed, megalopolis causes significant changes in mode of the physical fields both directly and indirectly. The violation of upper layer of soil in large-scale construction leads not only to change in landscape and groundwater regime, but also causes increased flow of underground fluids, including highly natural radon emanation which is dangerous for human. The results of instrumental observations indicate a significant influence of the megalopolis on the physical field in the surface atmosphere. The presence of man-made continuous and pulsed sources causes a significant increase in the amplitude of the physical fields, their spectral characteristics, as well as a violation of natural, nature-defined periodicity.
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Linearity Analysis of the Random Noise in Land Seismic Prospecting
More LessThe existence of the random noise is one of the main obstacles for getting higher-accuracy seismic records. The investigation of the seismic random noise properties is the pathway for improving the performance of noise attenuation algorithms. Here, we use the statistical testing methods to investigate the linearity of land-seismic-prospecting random noise, whereas the linearity, to some extent, can reflect the complexity of the generating process of the noise. The results show that the noise cannot be considered as a linear stochastic process. By analyzing the behaviors of the dataset, we obtain that the non-linear noise always have more energy in high frequency bands, and the energy distributions of the non-linear noise are disordered in high frequencies. Thus, the linearity of the random noise should be improved by attenuating the energy in high frequencies. We use an experiment to prove the correctness of our results. Based on the generating mechanism of the random noise, we also give a reasonable explanation for the results of our study. The findings have implications for future noise reduction and signal detection algorithms.
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ERT-SIP versus Seismic Tomography - Geophysical Mapping of a Planned Highspeed Railway Track, a Case Study from Norway
Authors J. Scheibz, A.K. Lysdahl, H. Anschütz, S. Kalstad and A.A. PfaffhuberWithin an infrastructure offensive in Norway the authorities plan and will build many hundred kilometers of new roads and rail tracks. One of the focuses is towards a high speed railway (HSR) system as a sustainable future transport. Due to the complex geology of large parts of Norway drilling campaigns often lead to a big question mark. To fill the gap between these drillings, reduce costs and improve planning security there is a demand in high resolution geophysical methods. NGI had the possibility to test, among other methods, high resolution ERT-IP and seismic refraction tomography to determine shallow bedrock (1-20 m) below a glacial infill on two test sites. While we assumed seismic refraction tomography to be the most reliable tool our study shows that our high resolution ERT model results in a lower deviation from existing drilling informations and supplementary revealed two steep weakness zones which were completely hidden in the seismic model. Additionally we calculated the spectral information of the IP data using the Cole-Cole relaxation model. The model provides additional information about the sedimentary cover but reveals contradicting informations about the weakness zones which cannot be further explained due to currently non-existing petrophysical models, especially for hardrock.
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Comparing Automatic and Manual Methods for Determination of the Bedrock Interface Using AEM Data
Authors H. Anschuetz, M. Voege, A. Kydland Lysdahl, S. Bazin, G. Sauvin, A. Pfaffhuber and A.L. BerggrenAn extensive airborne electromagnetic (AEM) survey was carried out in Norway with the primary purpose to obtain information of depth to bedrock in areas with little or no prior geotechnical knowledge. We present different approaches to extract a bedrock model from the high-resolution time-domain AEM data, including both automated and manual procedures. It is found that in the area of investigation a user-driven approach of manual bedrock picking is most suitable, taking into account the strongest vertical resistivity gradient and geological information as additional information. A semi-automatic, statistical method, called Localized Smart Interpretation (LSI), is presented and discussed in addition. This method, while not included in the original bedrock model for the entire area, proved promising and should thus be implemented in future projects of similar scope.
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Combination of Geophysical Technques to Characterize Sediments (Ebro Delta, Spain)
Authors B. Benjumea, A. Gabàs, A. Macau, F. Bellmunt, S. Figueras, M. Vilà and R. PiThe Ebro Delta (Spain) faces anthropogenic and climate changes that can cause a significant decrease on its subaerial surface. One of the causes of this reduction is subsidence that take place due to the compacting of the sediments. In order to identify zones vulnerable to subsidence, we have defined several targets such as: characterization of Holocene sediments (sands versus clays/silts and location of organics) and delineation of the bottom of deltaic sediments. Regarding these objectives, we have acquired geophysical data sets at different environments of the Ebro Delta (from delta plain to marshes among others). The methodology includes combination of seismic methods (surface waves, refraction and reflection methods) and electrical resistivity tomography for sediment characterization as well as the use of the H/V spectral ratio of microtremor measurements to delineate the base of the Holocene sediments. We show the results for one line located on the delta plain and close to alluvial fans. Geophysical models are characterized by a high-resistivity and high-velocity layer at around 25 m depth interpreted as the base of the deltaic sediments. H/V results provide evidence of maximum thickness of deltaic sediments located at the right side of the river mouth.
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Empirical Correlation of Shear Wave Velocity (Vs) with SPT of Soils in Madrid
Authors I. Pérez-Santisteban, A. Munoz Martin, A. Carbó and J.M. Ruiz-FonticiellaEmpirical correlations are usually used as a predictive tool in geotechnical engineering. However, equations calculated for soils very different to the ones to be characterized are frequently used, and so they are not representative of their mechanical properties. This fact, added to the increasing interest of civil engineering in knowing the shear wave velocity (Vs) of the ground, has led to the calculation of different empirical equations to predict the Vs value of the soils of Madrid. In this study this has been achieved by calculating the empirical correlations between the Vs value obtained through the ReMi (Refraction Microtremor) technique and the Standard Penetration Test (500 NSPT values). The empirical correlations proposed are applicable to the whole metropolitan area of Madrid, and have an excellent predictive capability due to the incorporation of the measurement depth to the equations, which has an important influence in the resistance properties of soils.
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The Rock Physics Template to Estimate Clay Content, Porosity, and Vulnerability of River Levees
Authors C. Konishi and Y. HashimotoWe propose to use the rock physics template to estimate clay content and porosity, and also introduce a new quantity that can be calculated from estimated clay content and porosity to represent vulnerability for the seepage failure of river levees. The rock physics template can be generated for a certain range of porosity and clay content by selecting appropriate rock physics models. This methodology provides clay content section, porosity section, and vulnerability sections from the integrated geophysical survey. We demonstrate the methodology to detect the most vulnerable location from the integrated geophysical investigations. The location identified as the most vulnerable point is verified by drilling and SPT. The location consists of very loose sand; therefore we concluded that the vulnerability section is beneficial to judge a priority of a treatment to stabilize the river levee.
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Combined GPR and Conductivimeter Prospection to Detect Internal Erosion under Mataró - Dike and Quay
Authors J.O. Caselles, J. Clapes, V. Perez-Gracia and J.A. CanasThis paper presents a case study of the Mataró port combining GPR and conductivimerter surveys. Mataró port has lots of slab drop off in the dike that was supposed to be produced by sea flow wash out fine soil particles. The combination of both methods applied at the dike and a quay has permitted to detect perfectly the location of voids and disturbed layers in it foundation. Also, results seem to indicate that the internal erosion it is not only produced by sea flow but also by interflow water form two old streams.
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GPR Analysis of Water Content in Concrete Specimen - Laboratory Test
Authors S. Santos-Assunçao, S. Krishna and V. Perez-GraciaApplications of Ground Penetrating Radar (GPR) in civil engineering context are popular and it has been widely used to characterize the media in terms of structural arrangement and pathologies. This work presents some tests carried out under laboratory conditions on a concrete slab. The aim of this study is to evaluate the moisture content in a homogeneous medium (concrete) using data obtained with a 1.6 MHz GPR centre frequency antenna. The evaluation process includes detailed analysis of the signal in both time and frequency domains. The key parameters are amplitude of surface reflection, changes in the centre frequency and attenuation of signal. The central frequency decreases in the A-scans obtained from zones with high water content. The amplitude of the first signal (reflection on the surface of the specimen) exhibits an increment. These results could be useful in the assessment of foundations and slabs, as well as in the evaluations of buried geological channels.
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A Magnetotelluric Study in La Rosa Diapir (Murcia, Spain)
Authors E. Gorriz, A. Marcuello, F. Escosa, P. Queralt, A. Martí, J. Ledo and E. RocaThe study of salt structures is an important challenge because of its economic implications. In this work La Rosa Diapir has been taken as an example of salt structure because is still active showing an outcrop in good conditions. This diapir is located on Eastern External Prebetic (in Jumilla, southeast Spain). The aim of this work was to perform a reconnaissance MT survey to obtain a first interpretation of the diapir area with this technique. This area is moderately populated and its geological structure is complex. The profile ran along NW-SE direction, and 16 stations were collected on it. The distance between them was approximately 800 m. The effect of the power lines were detected in the apparent resistivity curves, and the shift filters showed its capacity to reduce it. The dimensional analysis confirmed that the geoelectrical structure is 3D. Since the data have been recorded along a profile, the interpretation is based on the determinant of impedance. The results in the area indicate that the geoelectrical structure is quite conductive and no clear traces of resistive bodies can be seen.
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Can We Really Detect Cavities Using Seismic Surface Wave?
Authors A. Bitri, K. Samyn and C. FilippiShallow cavities, such as karstic caves in carbonate bedrock, near-surface underground mine workings and tunnels, constitute serious hazards for people and existing constructions due to the risk of collapse and subsidence. This phenomena is growing fast with climate change involving damages to buildings and increasing urban development costs. Karstic features, voids, surficial dissolution, alteration and unconsolidated material are thus major challenges for geophysical methods which could play a major role for their detection. Recent investigations have reported good results for cavity imaging using surface wave seismic methods (Sloan et al. 2015, Samyn et al., 2013, Leparoux et al., 2000, Nasseri-Moghaddam et al. 2005, Gucunski et al., 1996, Park et al. 1996). But in spite of successful case histories, business as usual void detection is still challenging due to the complexity of near surface materials and probably the limited resolution of geophysical methods. The propagation of Rayleigh waves in homogeneous layered media is well understood and has been addressed in depth by several authors (Thomson 1950, Haskel 1953, Graf 1975). The derivation of analytical solutions for the scattering of Rayleigh waves around heterogeneities is complicated and researchers often perform experimental tests or develop numerical models to study this problem (Gelis et al. 2005, Gucunski et al. 1996). These numerical studies have shown reflections from the heterogeneities (even in the cavities) and perturbations in the dispersion curves. Leparoux et al. (2000) applied the MASW test to locate two cavities: masonry at 3.0 m below the ground surface, and the other one embedded at about 8.0 m beneath the surface, without masonry. Xia at al. (2007) demonstrated using 2-D surface wave modeling that the diffractions due to a void on a homogenous half space were Raleigh-wave diffractions because of their amplitude, velocity, and frequency. They derived a travel-time equation of surface wave diffractions based on properties of surface wave and solved this equation for a phase velocity and depth to a void. Sloan et al. (2015) demonstrated the capability of using P-wave diffraction and surface wave backscatter techniques to detect subterranean tunnels. Despite these convincing arguments, we have been recently confronted to disheartening results leading us to the question: Can we really detect cavities using seismic surface wave? The objective of this study is to pose the problem for understanding interaction between a cavity and a Rayleigh wave by measuring the wave field in surface on the roof and on the floor of a known cavity. For addressing this issue, we have focussed on a study area located in Souzay-Champigny, France. This consists of an abandoned underground quarry network in cretaceous chalky limestone (Bitri et al. 2014). We have chosen these cavities because they are accessible underground and partly mapped.
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Determination of the Ground-building Relationships in the KTU Campus Area with Microtremor Measurements
Authors Y. Beker, N. Sayil, O. Akin and K.H. CobanMicrotremor measurement obtained by ground vibrations is one of the useful methods for determination of ground characteristics. Also the method has been using to specify building resonance risk during earthquakes in the last decades. In this study, single station microtremor recordings have been taken on the ground and at the 6 buildings in the KTU campus area. The measurements taken on the ground and in the buildings have been evaluated by Nakamura (H/V ratio) method. The eastern of the campus area presents Class-IV and the middle and western part of the campus present Class-II- Class-III according to Kanai and Tanaka ground classification. The predominant frequencies of the buildings are not in a harmony with the values of the ground. It can be deduce that the resonance risk is low for these buildings during the earthquakes. The H/V ratios of the ground change between 1-3 and lower than the buildings ratios which change between 5.0-8.5.
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Geophysical and Seismological Investigations around Cairo, Egypt
More LessCrustal movement studies are considered very important in the geodynamical research tools, which help in understanding the properties of the Earth in regional, global and local scales. The worldwide tool for such studies is the repeated geodetic measurements performed at chosen localities or regions. Recently, in Egypt, in order to monitor local, regional and global movements of crustal blocks, methods of space techniques were applied. There are two purposes for the study of crustal movements. The practical purpose includes checking the stability of structures, assessment of the degree of geological hazards and the detection of earthquakes. Scientific purpose is very important for understanding the deformation mechanism, testing new theories, which are applied to the design of structures. The most important applications are monitoring of the behavior of seismic active areas, deformations of the earth’s surface, earthquake prediction and deformation of huge constructions.
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Geotechnical Modelling of the Riyadh Metro Line 3 Using Multi-technique Geophysical Survey
Authors M. Cueto, S. Mayordomo, M. Martín, P. De La Puente, J. Olona and D. AriasThe Riyadh Metro Project is currently the largest public rail infrastructure project in the world under implementation. Metro will become the backbone of the city's public transport, significantly improving the life quality of citizens. We helped to carry out an exhaustive geophysical survey along the entire corridor of the Riyadh’s Metro Line 3. Among all the six Lines that the System comprises, Line 3 is the longest. It runs along 42 km, of which we identified about 13 km long underground sections (TBM EPBS and cut and cover) and 11 underground stations (cut and cover). The geophysical survey comprised a variety of field tests: seismic refraction, electrical resistivity tomography, ground penetration radar and seismic tests in boreholes (downhole and cross-hole testing). We correlated the results of the geophysical surveys with data coming from geological, hydrogeological and geotechnical investigations. This way, we delivered a continuous subsurface profile, which became the raw data for developing a full detailed geotechnical and hydrological model for the Line 3. The said model anticipated potential geotechnical risks (layers owning poor engineering parameters, karstic areas, faults or weaker rock volumes within the rock mass). Then, mitigations helped achieving, reliable, durable, safe and efficient designs and construction works.
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Application of Ground Penetrating Radar to Detect Sinkholes and Ground Subsidence in Beryanak, Tehran
Authors H. Gharahi, B. Yousefi and U. AladinAfter occurring two dangerous subsidence in both Arab and Pahlavani Streets located at Beryanak in the 10 districts of the municipality of Tehran, the GPR Department of Geotechnical & Strength of material study centre of Tehran had decided to use ground penetrating radar method to detect possible sinkholes and aqueducts on the site. The GPR data acquisition had been performed by a 50 MHz GPR antenna made by MALA Company. GPR data gathered in 7 longitudinal profiles parallel to the street directions. In the processing of the GPR data, different filters such as background removal, Migration, Band pass filter, and horizontal and vertical smoothing are applied to the data. The final result shows that the most of detecting sinkholes which cause to the subsidence were created due to the scouring. GPR profiles from Arab Street indicate that those anomalies were detected at shallow depths (between 2/5 to 5 m) are due to the subsidence caused by excavation and placement of sewer pipeline. But at some areas were identified from depths 8 to 15 meters can be some sinkholes and may lead to a big subsidence. These areas are very important for both studying and reconstructions.
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Engineering Foundation Characterisation of Wind Farm Site Using Integrated Data Approach - Clyde Perspective
By A. RichardWind Farm development across the UK has been on the rise for the past decade with potential for more works in many years to come as drive towards renewable and clean energy demands continue to grow. The challenges faced in poor ground conditions such as clay gouge underlying site infrastructure such as turbine foundation, access track, hardstands, control building etc can be key to providing a sustainable design option across the site. This study covers an integral approach using multiple site investigation datasets to inform design in both shallow and deep foundation solutions. The study revealed incorporation of multiple ground investigation data at a Wind Farm site with different juxtaposing local geology formations and the use of an informed decision to implement a shallow foundation option even in weaker ground conditions. Integrated data such as resistivity, seismic, borehole and trial pit logs, geotechnical laboratory results and in-situ testing were used to characterise Wind Farm sites in providing a more cost-effective and sustainable foundation solution. It is also important to note that data correlations generated from this study could well be extended into other sites where similar ground conditions exit.
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